The present invention relates to sound-attenuating mufflers for internal combustion engines and, more particularly, to sound-attenuating mufflers generating reduced back pressure.
Numerous muffler constructions have been proposed for the attenuation of the sound component of an exhaust gas stream from an internal combustion engine. Such mufflers are designed towards achieving appreciable sound attenuation, but without substantially increasing the back pressure on the engine, which results in power loss, reduced engine efficiency, and higher fuel consumption.
In surveying the prior art, U.S. Pat. No. 4,574,914 to Flugger teaches that although the patent art contains various muffler constructions which purport to solve the problem of sound attenuation without undesirable back pressure, in reality these various structures have substantial performance deficiencies. It is well known to provide a divergently tapered centrally located conical partition for flow of gases around the partition to effect an expansion of the gases. Typical of such structures are the devices shown in U.S. Pat. Nos. 2,071,351, 2,239,549 and 2,971,599.
Some of these patented mufflers follow such an expansion partition or cone with a contraction or concentrating partition or baffle. Typical of such devices are the mufflers shown in U.S. Pat. Nos. 1,081,348, 2,667,940, 3,029,895 and 3,029,896. These mufflers, however, do significantly increase back pressure by causing the exhaust gases to reverse the direction of their flow axially as they attempt to pass beyond the concentrating or converging baffle. This flow reversal may be effective in sound attenuation, but it has been found to increase back pressure undesirably.
Even mufflers which employ alternating divergent and then convergent partitions have suffered from undesirable bulk and/or weight, inordinate complexity, or auxiliary flow channels or openings in the partitions which defeat sound attenuation. Typical of such mufflers are the mufflers set forth in U.S. Pat. Nos. 624,062, 1,184,431, 2,325,905 and 2,485,555.
Thus, U.S. Pat. No. 4,574,914 to Flugger concludes that while the successive outward deflection and then inward convergence of gases in a muffler is broadly known in the prior art, such prior art structures typically have partitions or baffle structures which induce undesirable back pressure, contain openings or passageways which diminish the sound attenuating effectiveness of the muffler, or require excessive length, diameter and/or weight.
The muffler disclosed in U.S. Pat. No. 4,574,914 to Flugger is a compact, sound-attenuating muffler for a high-performance internal combustion engine in which the muffler casing has an elongated transverse cross-section with a height dimension of only slightly larger than the height dimension of the inlet exhaust pipe and a width dimension in the range of about 2 to 4xc2xd times the height dimension. The muffler includes a divergently tapering planar first partition which causes gases to be expanded only in a horizontal plane toward the side walls of the muffler and further includes a second partition formed to contract or converge the gases, in a horizontal plane toward a central opening. The first partition has a cup-shaped back surface so that contraction of the gases around the back side of the first partition is highly effective in attenuating sound, and both partitions are sloped in a direction toward the outlet from the muffler so as to minimize the generation of back pressure, which, purportedly, is not substantially greater than the back pressure in a straight pipe.
The muffler disclosed in U.S. Pat. No. 4,574,914 is designed explicitly for high-performance internal combustion engines for racing cars and the like. Although the back pressure generated by such mufflers is reported to produce a power loss of less than 2%, the sound level reduction associated with this power loss is from 130 db on the A scale to about 90 db on the A scale. A sound level of about 90 db on the A scale is completely unacceptable for common passenger vehicles and the like.
An improved muffler for an internal combustion engine having characteristically low back pressure and a pleasing sound is disclosed in my U.S. Pat. No. 6,286,623, which is incorporated by reference for all purposes as if fully set forth herein. The muffler includes an elongated housing having an inlet opening formed for the flow of exhaust gas into the housing and an outlet opening formed for the discharge of exhaust gas from the housing, and an inventive partition shaped like a hollow pyramid, disposed within the housing. The exterior surfaces of the pyramid are joined at a first end to form a pyramidal apex that points toward the inlet opening, and these surfaces extend at a second end to form a rugose base. The partition is disposed in the housing to form four distinct spaces between the rugose base and the housing for the flow of exhaust gas.
The reduced back pressure pleasing sound notwithstanding, there remains a recognized need for an exhaust system that further improves the sound attenuation while maintaining, and preferably reducing, the generation of back pressure. It would be of further advantage for the exhaust system to be of simple design, compact, lightweight, and easy to fabricate.
According to the teachings of the present invention there is provided a muffler for an internal combustion engine having characteristically low back pressure and a pleasing sound, the muffler having: (a) a housing including: (i) an inlet opening formed for a flow of exhaust gas into the housing, and (ii) an outlet opening formed for a discharge of exhaust gas from the housing; and (b) inner workings disposed within the housing, the inner workings including: (i) a dome-shaped partition having an exterior surface, a first end of the exterior surface pointing toward the inlet opening, and widening out at a second end to form a base, the dome-shaped partition having at least two partition openings disposed between the first end and the second end of the exterior surface, wherein the dome-shaped partition is disposed within the housing such that substantially all of the exhaust gas passing through the inlet opening is directed through the partition openings and into an interior of the dome-shaped partition, before being discharged through the outlet opening.
According to further features in the described preferred embodiments, the flow of the exhaust gas is deflected along the exterior surface in substantially all directions.
According to still further features in the described preferred embodiments, the partition openings are disposed in a side of the exterior surface.
According to still further features in the described preferred embodiments, the inner workings of the muffler further include: (ii) a converging partition having a flow outlet, the converging partition disposed within the housing such that the exhaust gas introduced through the partition openings and into the interior of the dome-shaped partition passes through the flow outlet.
According to still further features in the described preferred embodiments the exhaust gas passing through the inlet opening is directed along a main flow path towards the outlet opening, and wherein the inner workings are adapted such that the main flow path flow is solely in a positive orientation.
According to still further features in the described preferred embodiments, the inner workings are adapted such that any unidirectional flow regime within the housing bears solely a positive orientation.
According to still further features in the described preferred embodiments, the base of the dome-shaped partition is equipped with an outlet partition having an exhaust gas outlet for fluidly sealing the base, such that the exhaust gas introduced into the interior is discharged solely through the exhaust gas outlet.
According to still further features in the described preferred embodiments, with H1 defined as a height of the domed partition, and H2 defined as a height of at least one opening of the at least two partition openings, the ratio of H1 to H2 is less than 5 to 1.
According to still further features in the described preferred embodiments, with H1 defined as a height of the domed partition, and H2 defined as a height of at least one opening of the at least two partition openings, the ratio of H1 to H2 is at least 1.5 to 1.
According to still further features in the described preferred embodiments, the ratio of H1 to H2 is at least 2 to 1 and is less than 4 to 1.
According to still further features in the described preferred embodiments, the ratio of H1 to H2 is less than 3.5 to 1.
According to still further features in the described preferred embodiments, the ratio of H1 to H2 is at least 2.5 to 1 and is less than 3.5 to 1.
According to another aspect of the present invention there is provided a muffler for receiving and discharging an exhaust gas from an internal combustion engine, the muffler having: (a) a housing including: (i) an inlet opening formed for a flow of exhaust gas into the housing, and (ii) an outlet opening formed for a discharge of exhaust gas from the housing; and (b) inner workings disposed within the housing, the inner workings including: (i) a deflecting partition having an exterior surface, a first end of the exterior surface pointing toward the inlet opening, and widening out at a second end to form a base, the partition having at least two partition openings disposed between the first end and the second end of the exterior surface, wherein the partition is disposed within the housing such that substantially all of the exhaust gas passing through the inlet opening is deflected along the exterior surface and directed through the partition openings into an interior of the deflecting partition, before being discharged through the outlet opening.
According to still further features in the described preferred embodiments, the exterior surface is substantially convex.
According to still further features in the described preferred embodiments, the exterior surface is substantially hemi-spherical.
According to still further features in the described preferred embodiments, the exterior surface is substantially hemi-spheroidal.
According to still further features in the described preferred embodiments, the inner workings further include a guide trough, disposed along the exterior surface, for guiding the flow of the exhaust gas along the exterior surface and towards the partition openings.
The present invention successfully addresses the shortcomings of the existing technologies by providing a muffler that reduces back pressure appreciably relative to conventional mufflers of the prior art, including the muffler disclosed in my above-referenced patent, while achieving improved levels of sound attenuation. Moreover, the muffler of the present invention is of simple and reliable design, and is inexpensive to manufacture.